The invention relates to a method for operating a fuel supply system for an internal combustion engine, especially of motor vehicle, wherein fuel is pumped by a pump into an accumulator and wherein the pressure in the accumulator can be controlled (open loop and/or closed loop) by means of a pressure control valve. Furthermore, the invention relates to a fuel supply system for an internal combustion engine, especially of a motor vehicle, having an accumulator and a pump with which fuel can be supplied to the accumulator; and with a control apparatus for controlling (open loop and/or closed loop) the pressure in the accumulator by means of a pressure control valve.
Ever higher requirements are imposed on internal combustion engines, for example, of a motor vehicle, with respect to a reduction of the fuel consumption and the generated exhaust gases while, at the same time, wanting an increased power. For this purpose, modern internal combustion engines are provided with a fuel supply system wherein the supply of fuel into the combustion chamber of the engine is electronically controlled (open loop and/or closed loop) with a computer-supported control apparatus. Here, it is possible to inject the fuel into an air-intake manifold of the engine or directly into the combustion chamber thereof.
It is necessary that the fuel be injected into the combustion chamber under pressure especially in the last-mentioned type, the so-called direct injection. For this purpose, an accumulator is provided into which the fuel is pumped by a pump and is subjected to high pressure. From there, the fuel is injected into the combustion chambers of the engine via injection valves.
When starting the engine, the above-mentioned high pressure is mostly not present or is at least not immediately present. The starting of the engine must therefore be separately controlled (open loop and/or closed loop). Here, the peripheral conditions, which were already mentioned, such as reduced toxic substance discharge, are to be satisfied.
It is an object of the invention to provide a method for operating a fuel supply system for an internal combustion engine with which a starting of the engine as optimal as possible can be carried out.
This object is achieved in a method or a fuel supply system of the above-mentioned type in accordance with the invention in that the pressure control valve is closed when the engine is intended to be started but no rotational movement is yet present.
By closing the pressure control valve, a defined state of the engine is provided for the start operation, which is about to begin. Likewise, with this, it is achieved that the pressure in the accumulator no longer diminishes.
When the pressure control valve is closed by switching on the ignition and when, because of this switch-on of the ignition, the pump is also switched on for pumping the fuel into the accumulator, then this has the consequence that the pressure in the accumulator is dependent upon the pumping capacity of the pump and, if necessary, increases correspondingly. This especially advantageous for the intended starting of the engine.
The pressure control valve is at least partially opened in an advantageous embodiment of the invention when the engine is started and the first rotational movements are present. In this way, it is possible to control (open loop and/or closed loop) the pressure in the accumulator with the aid of the pressure control valve.
The pressure control valve is opened in dependence upon the temperature of the engine in an advantageous further embodiment of the invention. In this way, the pressure in the accumulator can be adapted to the temperature of the engine.
In another advantageous embodiment of the invention, the pressure control valve is opened in dependence upon the number of injections into the engine already carried out. In this way, the engine can be adapted in a simple manner to the course of the start operation.
In one embodiment of the invention, the pressure control valve is controlled (open loop and/or closed loop) in correspondence to a normal operation when a pregiven rpm limit is exceeded. In a simple manner, the transition of the control (open loop and/or closed loop) of the engine from the start operation into the normal operation is achieved.
The realization of the method of the invention in the form of a control element is of special significance with the control element being provided for a control apparatus of an engine, especially of a motor vehicle. Here, a program is stored on the control element which can be run on a computing apparatus and especially on a microprocessor and is suitable for carrying out the method of the invention. In this case, the invention is realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same manner as the method which the program is suitable to carry out. As a control element, especially an electrical storage medium can be used, for example, a read-only-memory.
Further features, applications and advantages of the invention become evident from the subsequent description of the embodiments of the invention which are shown in the figures of the drawing. All of the described or illustrated features define the invention with respect to themselves or in any desired combination independently of their relationship in the patent claims or their antecedent reference as well as independently of their formulation or presentation in the description or in the drawing.